// https://www.lintcode.com/problem/flatten-nested-list-iterator/description

/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * class NestedInteger {
 *   public:
 *     // Return true if this NestedInteger holds a single integer,
 *     // rather than a nested list.
 *     bool isInteger() const;
 *
 *     // Return the single integer that this NestedInteger holds,
 *     // if it holds a single integer
 *     // The result is undefined if this NestedInteger holds a nested list
 *     int getInteger() const;
 *
 *     // Return the nested list that this NestedInteger holds,
 *     // if it holds a nested list
 *     // The result is undefined if this NestedInteger holds a single integer
 *     const vector<NestedInteger> &getList() const;
 * };
 */
// class NestedIterator {
// public:
//     vector<int> vec;
//     NestedIterator(vector<NestedInteger> &nestedList) {
//         for(NestedInteger n: nestedList)
//         {
//             build(n);
//         }   
//     }

//     void build(NestedInteger n)
//     {
//         if (n.isInteger()) vec.push_back(n.getInteger());
//         else
//         {
//             for (NestedInteger nn: n.getList()) 
//             {   
//                 build(nn);
//             }
//         }
//     }

//     // @return {int} the next element in the iteration
//     int next() {
//         int tmp = vec.front();
//         vec.erase(vec.begin());
//         return tmp;
//     }

//     // @return {boolean} true if the iteration has more element or false
//     bool hasNext() {
//         return !vec.empty();
//     }
// };

class NestedIterator {
public:
    stack<NestedInteger> st;
    NestedIterator(vector<NestedInteger> &nestedList) {
        for (int i = nestedList.size() - 1; i >= 0; i--) {
            st.push(nestedList[i]);
        }
    }

    int next() {
        int ans =  st.top().getInteger();
        st.pop();
        return ans;
    }

    bool hasNext() {
        while (!st.empty()) {
            if (st.top().isInteger()) {
                return true;
            }
            vector<NestedInteger>  nestedList = st.top().getList();
            st.pop();
            for (int i = nestedList.size() - 1; i >= 0; i--) {
                st.push(nestedList[i]);
            }
        }
        return false;
    }
};

/**
 * Your NestedIterator object will be instantiated and called as such:
 * NestedIterator i(nestedList);
 * while (i.hasNext()) v.push_back(i.next());
 */